1. Field of the Invention
This invention relates to the field of electrodynamic systems, such as electrical generators or motors. More specifically, this invention relates to an improved axial zone block assembly for maintaining a pressure differential in the end turn area of a rotor in such a system.
2. Description of the Prior Art
In certain electrical generators which are manufactured by the assignee of this invention, Westinghouse Electric Corporation, high and low pressure zones are intentionally designed within the system to induce the flow of coolant through certain heat generating components of the system.
FIG. 1 depicts a portion of an electrical generator according to a prior art design. Specifically, FIG. 1 depicts a prior art axial zone assembly 10, shown positioned adjacent to a stationary stator 12. A rotor shaft 14 is mounted to rotate with respect to and within stator 12. A plurality of end turns 16 are mounted to an end of rotor shaft 14.
To separate an intended high pressure zone on one side of rotor shaft 14 from a low pressure zone on an opposite side, an axial baffle block 24 is positioned in a slot 17 that is defined in an end length of rotor shaft 14. Slot 17 is defined in rotor shaft 14 by a slot bottom 18, and has a depth which is equal to the distance between slot bottom 18 and an outer diameter 20 of rotor shaft 14. A steel ripple spring 22 is positioned between rotor shaft 14 and the bottom of axial baffle block 24.
During normal operation of the electrical generator, rotor shaft 14 rotates at high speed relative to stator 12. End winding 16, baffle block 24, and spring 22 rotate as a unit with rotor shaft 14. At high speed rotation, centripetal acceleration forces baffle block 24 against end turns 16. However, at low speed rotation, baffle block would tend to be able to move between slot bottom 18 and end turns 16 were it not for the presence of spring 22. Spring 22 effectively biases baffle block 24 against end turns 16 during low speed rotation, preventing such movement.
However, spring 22 is susceptible to fatigue after long term operation of the generator. During high speed rotation, centripetal acceleration may cause spring 22 to deflect under its own weight, putting a fatigue-inducing stress on spring 22. If not replaced at proper intervals, spring 22 may break, and fragments can possibly migrate axially out from between baffle block 24 and slot 17. Once a spring fragment is no long constrained by the baffle block 24, it may become objective metal inside the generator, which can be very destructive.
It is clear that there has existed a long and unfilled need in the art for an improved axial zone assembly and an electrodynamic system which is less susceptible to fatigue related damage, and which is less destructive to the system if fatigue related damage should occur.